1. Field of the Invention
Embodiments of the present invention generally relate to a sputtering apparatus for forming films on large area substrate such as flat panel, large screen televisions, and solar panels.
2. Description of the Related Art
As demand for larger flat panel display screens increases, so must the sputtering target area. As the sputtering target become larger, it becomes increasingly more difficult to adequately provide a uniform distribution of reactive gas to the sputtering target. In the past, reactive gas has been introduced to the sputtering chamber through a gas inlet. The gas inlet is typically located on the side of the chamber. With an increase in target size, the reactive gas tends to not adequately reach the center of the target. When the reactive gas does not uniformly reach the entire target, the film deposited on the substrate will not have a uniform composition across the substrate. For a large area sputtering targets with the gas introduced from the periphery of the target, the gas concentration is highest at the chamber wall where the gas inlet is located. The gas concentration decreases moving across the chamber to a low point in the center of the chamber.
U.S. Pat. No. 5,346,601 to Barada et al. shows a sputtering apparatus in which two gas introduction tubes are provided within a collimator. The gas introduction tubes are perpendicular to each other and within the same plane. The gas tubes extend across the processing area. By providing the gas introduction tubes within the collimator, the reactive gas can adequately be provided to the substrate while not shadowing the wafer from sputtering material. A plurality of gas outlets are present across the tube. In order to remove the gas tubes, the entire collimator structure must be removed. The collimator cannot be removed without also removing the gas tubes.
As shown by Barada et al., sometimes gas introduction tubes can extend across the processing space between the target and the substrate. The gas introduction tubes, such as that used by Barada et al., usually only introduce gas through a series of gas outlet holes formed in a gas introduction tube. A problem with prior art gas introduction tubes is that they must provide the gas at a high pressure through the tube in order to have a uniform pressure passing through the tiny holes in the tube. When the process is stopped and the gas is stopped, gas will continue to flow out of the holes because of the pressure buildup within the tube. The gas will continue to disperse into the processing chamber even after the process has stopped. The excess gas introduced into the chamber may contaminate the wafer or cause further, undesirable reactions with the substrate.
There is a need in the art to provide reactive sputtering gas to a chamber uniformly across a large area sputtering target. There is also a need in the art to provide easily removable reactive gas introduction tubes without disassembling the sputtering chamber.